Pregnant women exposed to pesticides have children with slightly lower IQ, studies show

Pesticides on fruits and vegetables may be harmful to a developing fetus — slightly. Children whose mothers were exposed to low doses of a specific class of pesticides may have a slightly lower IQ in later childhood, three new studies suggest.

The new research found children had a slightly lower IQ by age 7 if their mothers, mostly low-income and mostly Latina and black, had higher-than-average exposure in pregnancy to organophosphates, pesticides farmers still sometimes spray on fruits and vegetables. But some of the data are not as conclusive as they might seem at first glance.

All three studies, published Thursday in Environmental Health Perspectives, measured the presence of organophosphates in the mother’s urine or blood during pregnancy. Women could have ingested the pesticides by way of food or breathing the air — the pesticides were once common in households before the EPA banned their use in 2002, but in inner cities, these insecticides were still common in the mid-2000’s to control insect infestations. In the three studies, the children took an IQ test around age 7 that measured working memory and reasoning abilities.

In one study, researchers from Columbia University found that African American and Dominican women in New York City with the highest levels of chlorpyrifos, a type of organophosphate, in their umbilical-cord plasma had children with a slightly lower IQ by age 7 compared with those whose mothers had lower exposure — for every large increase in pesticide exposure, the children had about a 1- to 2-point decrease in IQ and 2- to 4-point decrease in working memory.

In another study, among Latinas and African American women in New York City, researchers from Mount Sinai found women with the highest levels of organophosphates in their urine had children with a slightly lower IQ — for every tenfold increase of a pesticide marker in the mother’s urine, children had a 3-point IQ drop at age 7.

And in a study of Mexican women in the agricultural town of Salinas, UC Berkeley researchers measured pesticide exposure in the urine of pregnant women and found a 7-point IQ discrepancy between children whose mothers had the highest exposure compared with those who had the lowest.

Many of the women were poor, and socioeconomic status is linked to lower IQs, so researchers in some of the studies controlled for variables such as income. Women were compared with other women in the data set, not a national average. And the exposure levels were low in all the studies — in the Columbia study, 43% of the women had levels that were undetectable, and in the Berkeley study, the median exposure was slightly above the national average.

The studies are the first to measure how low levels of pesticides affect children while they are still developing in the womb, said Brenda Eskenazi, a lead author on the Berkeley study, in an interview. Previous research looked at children, not fetuses, exposed to high levels of pesticides.

Organophosphates are known to affect the brain in animal studies, so their effect in children may be more potent while they are still developing, says Rudy Rull, a research scientist at the Cancer Prevention Institute of California in Fremont.

“These studies present compelling evidence of the potential effects on children’s neurodevelopment from exposure to chlorpyrifos and other organophosphate insecticides,” said Rull in an email.

But let’s be cautious—the IQ differences were small, and some only appeared by looking at the data in a certain way.

Women in the Berkeley study, for example, had their urine measured for traces of pesticides twice—once in the first half of pregnancy and once in the second half. The researchers found no correlation between IQ and pesticide markers in the first urine test or in the second urine test. But then when they averaged the two, voila—a correlation.

It’s not the best way to measure how much pesticide exposure the women really had, acknowledges Eskenazi. The chemicals the researchers measured in the urine—called DAP metabolites—disappear within days or hours of exposure.

“My feeling is, we don’t have a super-good measurement of organophosphates during pregnancy, especially when there are lot of different ones they are exposed to,” she said.

That calls into question the 7-point difference in IQ between women with “high” levels of exposure versus those with “low” levels.

“It’s enough to say, there are definitely limitations to the measurement, and I think that’s the reason why given that epidemiology is imperfect, you want to see convergence of findings and consistency among what you see in animals and humans,” says Eskenazi.

She says the take-home message for most pregnant women isn’t that they should stop eating fruits and vegetables, a common source of exposure. They should just wash them carefully, even using a brush to scrub them, she says.

Even Eskenazi says:

“In terms of the bigger picture, we have to weigh the potential negative effects of limiting the use of some pesticides in agriculture against the positive effects of using them if it means more food, and more accessible food, and lower priced food because we want to make sure there are adequate food resources for the whole country.”